This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-382550, filed Dec. 15, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to a suspension for disc drive incorporated in an information processing apparatus, such as a personal computer.
In a disc drive that is provided with a rotating magnetic disc or magneto-optical disc, a magnetic head is used to record on or read data from a recording surface of the disc. The magnetic head includes a slider opposed to the recording surface of the disc, a transducer stored in slider, etc. When the disc rotates at high speed, the slider slightly lifts off the disc, whereupon an air bearing is formed between the disc and the slider. A suspension for holding the magnetic head comprises a beam member called a load beam, a flexure formed of a very thin plate spring fixed to the load beam, a base plate provided on the proximal portion of the load beam, etc. The slider that constitutes the magnetic head is mounted on the distal end portion of the flexure.
In a hard disc drive (HDD), the track center of the disc must be subjected to following control within xc2x110% of the track width. With the recent development of higher-density discs, the track width has been being reduced to 1 xcexcm or less, and it is hard to keep the slider in the track center. It is necessary, therefore, to carry out accurate position control of the slider as well as to increase the stiffness of the disc, thereby reducing the oscillation of the disc.
In general, conventional disc drives are of a single-actuator type such that a suspension is moved by means of a voice coil motor only. The single-actuator suspension has many peaks of resonance in low-frequency bands. Thus, it is hard to control a slider (head portion) on the distal end of the suspension in high-frequency bands by means of the voice coil motor only, and the bandwidth of a servo cannot be enhanced.
Accordingly, a dual-actuator suspension has been developed including a micro-actuator portion as well as a voice coil motor. The distal end portion of a load beam or a slider is slightly moved by a second actuator of the micro-actuator portion in the transverse direction of the suspension (so-called sway direction).
Since the movable portion that is driven by means of the second actuator is considerably lighter in weight than a movable portion of the single-actuator suspension, the slider can be controlled in high-frequency bands. Thus, the dual-actuator suspension, compared with the single-actuator suspension, can make the bandwidth of a servo for the position control of the slider several times higher, and track misses can be reduced correspondingly.
It is known that a piezoelectric ceramic element, such as lead zirconate-titanate (solid solution of PbZrO3 and PbTiO3) called PZT, can be suitably used as the material of the second actuator. Since PZT has a considerably high resonance frequency, it is suited for the second actuator that is used in the dual-actuator suspension.
Piezoelectric ceramic elements such as PZT are fragile and breakable, and besides, contamination that is attributable to the generation of particles from the element surface constitutes a hindrance to practical use. If these particles get into the space between the slider and the disc that is rotating at high speed, the disc and the slider are damaged, so that data recorded on the disc may be broken or a crush may be caused.
The inventors hereof conducted a test for examining the way of generation of particles from a suspension that uses piezoelectric ceramic elements. In this test, the suspension was washed in a liquid by means of an ultrasonic cleaner, and particles not smaller than a given size in a given quantity of liquid were counted. In consequence, it was found that the suspension that uses the piezoelectric ceramic elements produce more particles than a conventional suspension that uses no piezoelectric ceramic elements does.
In the piezoelectric ceramic elements, metal layers for electrodes are formed individually on the obverse and reverse sides by sputtering or plating. Accordingly, there is hardly any possibility of particles being generated from the obverse or reverse side of the element. Since the side or end faces of each piezoelectric ceramic element are cut by means of a dicing machine or the like in a manufacturing process, they are exposed cut surfaces. These cut surfaces form sources of particles, so that particles continue to be generated every time the suspension is cleaned.
Accordingly, the object of the present invention is to provide a suspension for disc drive with a micro-actuator portion capable of restraining generation of particles.
In order to achieve the above object, a suspension of the present invention comprises a load beam provided with a flexure, an actuator base provided on the proximal portion of the load beam, a piezoelectric ceramic element mounted on the actuator base and adapted to be distorted to displace the load beam in a sway direction when voltage is applied thereto, and a cover portion formed of a covering material filling the space between the peripheral edge portion of the piezoelectric ceramic element and the actuator base and covering the longitudinally opposite end faces and side faces of the piezoelectric ceramic element. The covering material may be a synthetic resin or metal that can be fixed to the piezoelectric ceramic element, including an adhesive agent, for example. According to this invention, the cover portion can restrain generation of particles from the element. Since the cover portion cannot substantially hinder the displacement of the piezoelectric ceramic element, it never causes the stroke of the element to deteriorate.
In the suspension of the invention, the actuator base may be formed having an opening portion capable of holding the piezoelectric ceramic element, the opening portion holding the piezoelectric ceramic element. Since the piezoelectric ceramic element is held in the opening portion of the actuator base, according to this invention, a sufficient quantity of covering material can be easily applied on the end and side faces of the element, and the covering material can be prevented from running down before it is cured. Thus, the resulting cover portion can be thick enough.
In the suspension of the invention, moreover, the load beam and the actuator base may be connected to each other by means of an independent flexible hinge member. According to this invention, materials that meet required properties of the load beam, actuator base, and hinge member can be used, so that the properties of the suspension can be improved.
In the suspension of the invention, an extending portion extending along a side face of the piezoelectric ceramic element may be provided on a part of the hinge member, and the cover portion may be formed along the extending portion. According to this invention, a covering material such as an adhesive agent can be easily supplied along the extending portion on the hinge member and can be prevented from running down, so that the resulting cover portion can be thick enough.
In the suspension of the invention, the covering material may be an adhesive agent with uncured-state viscosity ranging from 2 PaS to 1,000 Pas. According to this invention, the adhesive agent for the formation of the cover portion may be applied thick on the piezoelectric ceramic element and has moderate fluidity, so that it enjoys good applicability.
In the suspension of the invention, furthermore, the covering material for forming the cover portion may be formed of the same adhesive agent that is used to fix the piezoelectric ceramic element to the actuator base. According to this invention, a common adhesive material can be used for the adhesive agent for fixing the piezoelectric ceramic element to the actuator base and the adhesive agent for forming the cover portion, so that the adhesive agent can be handled with ease, and working properties for applying the adhesive are improved.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.